Amyotrophic lateral sclerosis (ALS) is a progressive, late-onset neurodegenerative disorder for which there is currently no effective treatment, and which affects nearly 30,000 people in the United States. A subset of ALS cases are caused by mutations in the ubiquitous antioxidant enzyme Cu, Zn superoxide dismutase (SOD1) through an ill-defined toxic gain of function. The accumulation of misfolded and/or aggregated SOD1 in dying motor neurons suggests that SOD1-related ALS is primarily a protein deposition disorder. However, little is known about the causes, mechanism, and consequences of SOD1 oligomerization in ALS. The long term objective of the proposed work is the elucidation of the mechanism(s) by which SOD1 forms non-native oligomers. As ALS symptoms typically do not appear until late in life, we hypothesize that factors in the cellular environment likely influence oligomer formation and subsequent motor neuron toxicity. In the aims proposed here, we will examine the effect of two physiological post-translational modifications, phosphorylation and glutathionylation, on the structural transitions of SOD1 from native to aggregated states. The first specific aim will focus on the first step in oligomer formation, dissociation of the native SOD1 homodimer. Crystal structures of modified SOD1 will be solved and assessed for any perturbations in the dimeric structure. Aim 2 will test the effect of modification on the oligomerization dynamics of wild type and mutant SOD1. Biophysical techniques such as surface plasmon resonance and size exclusion chromatography will be used to monitor the rate of dimer dissociation and appearance of non-native oligomeric species. By studying modified and unmodified forms of wild-type SOD1 as well as a diverse set of ALS-associated mutants, we will determine whether modifications and mutations produce a cumulative increase in SOD1 aggregation propensity. The studies proposed here would enhance the currently meager understanding of the general SOD1 oligomerization pathway and provide novel insight on how this process is affected by physiological post-translation modifications. As aggregation is a central pathological feature of SOD1-related ALS, knowledge of this process and its cellular determinants would lead to more effective treatments and preventative measures.